The invention provides processes for recovering zein from corn. The processes and apparatus of the invention are designed to be implemented as additional modules in pre-existing ethanol production plants, and can easily be incorporated into new constructions as well.
Zein is a protein found in corn, millet (also called milo), rice and other plants which has many applications in industry. Zein has many uses and can be used to make a variety of different products. Much of the zein produced today comes from corn and is used in livestock food as a protein source. Another useful product that can be made from zein is a biodegradable resin (polymer), which can be used as a substitute for existing plastic products, e.g., edible film barriers for food products, or edible food wraps. Zein is also used in the pharmaceutical industry as a tablet coating and in the food industry as a fat replacer. Other uses are likely to be developed, as the availability of zein increases.
There are many known techniques for recovering zein as well as other natural ingredients such as oil, from corn. U.S. Pat. No. 4,716,218 to Chen et al. describes a process for producing grain oil, dehydrated alcohol, grain protein such as zein and starch utilizing ethanol extraction. The process for the production of grain oil and dehydrated alcohol by cracking the grain; drying the grain to a moisture content sufficiently low to enable the grain to dehydrate an ethanol solution to greater than 90% ethanol, while simultaneously extracting the grain oil from the dried grain with an ethanol solution of greater than 90% ethanol, and recovering the grain oil and dehydrated alcohol from the extractant. In a preferred embodiment, cracking the grain, drying the grain to a moisture content sufficiently low to dehydrate an ethanol solution of greater than 90% ethanol while simultaneously extracting oil from the dried grain with a first ethanol solution of greater than 90% ethanol, recovering oil and dehydrated alcohol from the first extractant, extracting grain protein from the residue of step with a second ethanol solution wherein the ethanol concentration is that which maximizes the protein solubility, recovering the protein from the second extractant, recovering starch from the residue of step.
U.S. Pat. No. 5,410,021 to Kampen describes and claims a process for recovering protein, protein isolate or starch from cereal grains such as corn that utilizes wet attrition milling to break the protein-starch bonds while leaving the starch granulates intact. Kampen""s process includes recovering protein from cereal grains containing starch and protein bound into a matrix by the grinding said grains to a particle size appropriate for introduction to a wet attrition mill; defatting said grain; wet attrition milling particles of said grain to a size sufficiently small to break the bond between starch and protein, then extracting the broken bond protein from the starch with at least one solvent, then separately the resulting high liquid content portion containing the extracted protein from the resulting high solids content portion containing the starch, and then subjecting the high liquid content portion containing the extracted protein to continuous cross-flow microfiltration with inorganic membranes for isolating the protein constituent, concentrating the protein constituent into a dry power.
U.S. Pat. Nos. 5,254,673 and 5,580,959 to Cook disclose extraction of zein, zein bodies, glutelins or destarched corn gluten from corn gluten veal by enzymatic starch hydrolysis with an amylase, alkaline treatment, alcohol washing and alcohol extraction to yield a starch-free, deflavored and decolored zein. The method includes the steps of removing color and flavor impurities from the gluten by treating corn gluten with alkali to remove fatty acids and corn oils contained therein and then with an aqueous alcoholic solvent having a concentration which does not substantially extract zein, zein bodies and glutelins therefrom, thereafter changing the concentration of the alcoholic solvent to a concentration sufficient to separate the gluten into decolored and deflavored zein or zein bodies and glutelin fractions.
U.S. Pat. No. 4,486,353 to Matzuzaki et al. discloses a specific process of extracting vegetable oil and fats from oleaginous raw material such as corn germ by obtaining flakes having a moisture content of from 0.7 to 10 weight % from an oleaginous raw material, said flake being characterized by the absence of an impervious outer hull or coat; contacting said flakes with an ethanol solution containing not less than 90 weight % ethanol at a temperature in the range from 70xc2x0 C., to the boiling point of said ethanol solution, thereby obtaining a miscella, cooling said miscella, thereby obtaining vegetable oil or fat or both, and a separate defatted miscella; drying said defatted miscella with a molecular sieve material having a pore size from 3 xc3x85 to 4 xc3x85, thereby obtaining a second ethanol solution wherein said second ethanol solution contains less than 7 weight % water; and using said second ethanol solution as the ethanol solution of said contacting step in a second extraction.
U.S. Pat. No. 5,773,076 to Liaw et al. is directed to a wet milling process in which gluten is recovered from steep water by membrane filtration and is then incorporated into a corn gluten meal product. The process of recovering insoluble gluten protein from steep water in a corn wet milling process includes steeping corn kernels in an aqueous solution that comprises gluten wash water, thereby producing steep water which contains insoluble gluten protein; membrane filtration of the steep water, thereby producing a retentate which has a higher concentration of the insoluble gluten protein than the original steep water; reducing the water content of the retentate; and incorporating the remaining retentate into a corn gluten meal product.
U.S. Pat. No. 5,342,923 to Takahashi et al. describes a process for refining zein with a high purity acetone solution by dispersing a solution containing crude zein into a solution comprising acetone in which said zein is insoluble; thereby precipitating a zein component as porous solids; separating said porous solids; and drying said solids.
U.S. Pat. No. 5,510,463 to Takahaski et al. discloses a process for producing zein wherein zein and pigment components are extracted from a corn gluten meal that has been treated with a C5-C9 hydrocarbon solvent. The zein is extracted by subjecting the treated corn gluten meal with a solvent having 91-96% by volume ethanol. The zein and the pigment components are then separated from the extract solution. Oil and fat components and pigment components may be extracted prior to the zein extraction steps.
U.S. Pat. No. 5,367,055 to Takahashi et al. discloses a process for treating a zein containing material to decrease inherent color and smell and to obtain zein by contacting the material with an aqueous acetone solution having an acetone solution which xe2x80x9ccauses almost no dissolutionxe2x80x9d of the zein compound. The process includes the steps of contacting the zein-containing material with (1) a 80-100% (V/V) acetone solution at a temperature of 25-60xc2x0 C., or (2) a 70-80% (V/V) acetone solution at a temperature of 25-40xc2x0 C., and separating the resulting solid from the solution.
U.S. Pat. No. 4,624,805 to Lawhon describes a process for recovering food grade protein from agricultural commodities, e.g., corn, prior to alcohol production. The process includes the steps of obtaining a suitable agricultural commodity in a form suitable for extraction of protein; extracting protein from said agricultural commodity with an alkali solution which forms a dispersion with said agricultural commodity; separating the dispersion into a solids fraction and a liquids fractions, said liquids fraction containing extracted protein; removing the protein from said liquids fractions by ultrafiltration using a membrane having a molecular weight cutoff between about 10,000 and about 30,000 daltons; and utilizing said solids fraction for alcohol production.
The process of the present invention provides a simple method for recovering zein from corn in alcohol production plants using ethanol as a solvent. Since the solvent, ethanol, is produced right at the plant, there is a plentiful supply of solvent, which is, in preferred embodiments, recovered so that there is almost no solvent waste. The process includes the steps of preparing an ethanolic zein extract by mixing a zein-containing substrate with hydrous ethanol to separate carbohydrates and other impurities from the zein fraction; removing suspended solids from the zein extract to yield a crude zein fraction; purifying the crude zein extract by contacting the crude zein extract with an adsorbent that adsorbs impurities; e.g., oil, ash, color or any remaining carbohydrates to yield a purified zein fraction, separate the adsorbent and adsorbent impurities from the zein fraction, and recovering the purified zein fraction. In preferred embodiments, the adsorbent is activated carbon.
In a preferred embodiment, prepared whole-grain corn is extracted using continuous counter current extraction with aqueous ethanol as the extraction solvent. This invention would be applied as an add-on module to an existing ethanol production facility or as an integral part of a new ethanol production facility. The method of the invention applies: (1) dry milling of tempered whole grain corn; (2) screening of the milled corn to remove fines; (3) cold flaking the screened meal; (4) extraction of zein and other corn components with a 75 percent by weight ethanol solution; (5) recovery of the ethanol solvent using water displacement so that the ethanol can be reused in the process; (6) recovery of the extracted corn flakes for use as feed stock for the ethanol plant using enzyme starch liquefaction technology to form a thinned (100 to 900 centipoises) meal slurry; (7) recovery of residual ethanol in the liquefied, extracted flakes by surface contact condensation; (8) treatment of the crude zein extract with adsorbent materials; (9) filtration of the adsorbent/extract mixture to remove the adsorbent, impurities, and color from the extract; (10) regeneration of the adsorbent for reuse in the process; (11) spray drying the refined and decolorized zein extract to produce a light to near-white zein powder containing 60 to 80 percent by weight protein; (12) recovery of the ethanol from spray drying for reuse in the process; (13) treatment of the spray dried zein product with ethanol and/or water to further refine the zein; (14) drying the refined zein to produce a white zein product containing from 85 to 99 percent by weight protein; (15) reconcentration of all dilute ethanol streams generated by the process so that the ethanol can be reused in the process as extraction solvent. Additional detail is provided in the steps below and in the attached process schematic, FIG. 1.
The invention also relates to a sliding cell extractor having a moving bed which is adapted for counter current extraction. This extractor is illustrated in FIG. 2. Extractor 1 includes a first extraction section 2 which begins in upper cell deck 1a and continues in the bottom cell deck (10a-10h) and a second extraction section 3 located in the bottom cell deck 1b (11a-11d). A transportable (sliding) cell or cell bed 4 contains the substrate from which the zein will be extracted, and transports the substrate by, e.g., a rotatable sprocket/chain mechanism, from the first to the second extraction section. First inlet pipe 10 communicates with first extraction section 2 for introducing a first solvent therein, and, similarly, second inlet pipe 11 communicates with the second extraction section 3 for introducing a second solvent therein. Recovery pipe 12 communicates with second extraction section 3 to recover the solvent that drained by gravity fed to the bottom of the extractor. Typically the recovery pipe will be located in the floor of the extractor section. In preferred embodiments, to enhance the economics of the operation, the distal end 12a of recovery pipe 12 communicates with first extraction section 2 and recycles the recovered solvent therethrough. The second solvent will usually be water so that the remaining alcohol in the substrate is recovered.
Optionally, an alcohol inlet pipe 15 communicates with recovery pipe 12a prior to the distal end of the recovery pipe 15a so that alcohol may be introduced into the recycled solvent so that the alcohol content of the recycled solvent may be adjusted to an appropriate value prior to entry into the first section. In operation, moving cell bed 4 transports the zein bearing substrate though a series of counter current extraction steps. Other counter current extractors are available and can be readily adapted for use in the process. Particularly preferred is the Lurgi SC sliding cell extractor.
In operation, hydrous ethanol is added via inlets 10a-10h in a series of counter current extraction stages such that clean ethanol containing little or no zein is added to the end of substrate bed 10a which has the lowest zein concentration and the most concentrated zein extract is added to the feed end 10h of the substrate bed, which has the highest zein concentration. Extractor 1 can add a second extraction medium in the last stages of the substrate bed such that the second medium, e.g., water, displaces the first extraction medium of hydrous ethanol to recapture the solvent for reuse in the cycle without having to dry the substrate. This optional recycling step greatly enhances the economics of this method.
The invention is described in more detail below.